Vision impairments such as myopia (i.e. near-sightedness), hyperopia (i.e. far-sightedness) and astigmatism can be corrected using eyeglasses or contact lenses. Alternatively, the cornea of the eye can be reshaped surgically to provide the needed optical correction. For example, it is known that if part of the cornea is removed, the pressure exerted on the cornea by the aqueous humor in the anterior chamber of the eye will act to close the void created in the cornea, resulting in a reshaped cornea. By properly selecting the size, shape and location of a corneal void, the desired shape, and hence optical properties of the cornea can be obtained.
One procedure employed to reshape the cornea is to remove portions of the anterior portion of the cornea. For example, see U.S. Pat. No. 4,665,913 which issued to L'Esperance for an invention entitled “Method for Ophthalmological Surgery,” and U.S. Pat. No. 4,669,466 which issued to L'Esperance for an invention entitled “Method and Apparatus for Analysis and Correction of Abnormal Refractive Errors of the Eye.” Another procedure used to reshape the cornea removes and reshapes subsurface tissue such as stromal tissue. As an example of such a procedure, U.S. Pat. No. 4,907,586, which issued to Bille et al. for an invention entitled “Method for Reshaping the Eye,” discloses an intrastromal photoalteration technique for reshaping the cornea. Importantly for the purposes of the present invention, the above cited Bille patent discloses the use of a pulsed laser beam for photoalteration of intrastromal tissue. As disclosed by Bille, the pulsed laser beam penetrates corneal tissue and is focused at a point below the surface of the cornea to photoalter stromal tissue at the focal point. The ability to reach a subsurface location without necessarily providing a physical pathway allows for great flexibility in corneal reshapings and can reduce the total amount of tissue disruption required for a particular corneal reshaping. Further, as the prescribed corneal void shape becomes more complex and precise, the need to access subsurface tissue without a physical pathway becomes more important.
Recently developed so-called LASIK procedures incise the anterior portion of the cornea using a microkerotome to create a flap. It should be recognized that a microkeratome is a mechanical device that uses an automated blade to create a flap. Once created, the flap can be temporarily lifted for photoalteration of the exposed stroma. This procedure, like the procedure disclosed in Bille et al. '586, has as its objective the removal of only stromal tissue with the consequent preservation of anterior corneal tissue. As discussed above, the LASIK procedure relies on a physically prepared pathway, and hence is limited to simple flap configurations. In contrast with the simple flap configurations which can be prepared using a microkerotome, the procedure of the present invention recognizes that a pulsed laser beam can be focused below the surface to create complex flap designs.
In light of the above, it is an object of the present invention to provide a method for corneal laser surgery that corrects the refractive characteristics of the cornea by removing only stromal tissue and minimizes the total amount of tissue undergoing photoalteration. Another object of the present invention is to provide a method for corneal laser surgery which creates a corneal flap having a complex peripheral edge such as a peripheral edge which can be repositioned in an interlocking relationship with undisturbed corneal tissue to hold the corneal flap in place during subsequent healing, or a peripheral edge that incorporates a tab to assist in lifting and repositioning the corneal flap. Still another object of the present invention is to provide a method for corneal laser surgery which creates a corneal flap that can be lifted to expose and then photoalter a bed of stromal tissue that has a complex shape, such as a convex, concave or irregularly shaped bed. Yet another object of the present invention is to provide a method for corneal laser surgery which is relatively easy to practice and comparatively cost effective.